1. Field of the Invention
The present invention relates to a solid-state image pickup device, particularly to a solid-state image pickup device used in a scanner, video camera, digital still camera or the like.
2. Description of the Related Art
In recent years, there have been available image input apparatuses such as a digital camera, video camera and image reader. A CCD image sensor or a solid-state image pickup device called non-CCD image sensor such as a bipolar transistor image sensor, FET image sensor or CMOS image sensor are provided in an image input apparatus. A solid-state image pickup device converts optical image information into electrical signals. The obtained electrical signals are subjected to various types of signal processing and displayed on a display or recorded on a storage medium.
Solid-state image pickup devices of today which use an amplifying MOS sensor generally adopt progressive scanning, which scans each line, or row of pixels, in a sequential order. In order to support current television standards such as NTSC and PAL, means for adding pixel signals in the vertical direction in an image-pickup device are proposed. For a high-resolution solid-state image pickup device, there is proposed means for adding pixel signals in the vertical direction and horizontal direction in a solid-state image pickup device to read out, at high speed, signals of an image with a relatively low resolution into an electronic viewfinder, a small screen for monitoring or the like.
A CMOS sensor circuit having adding means is disclosed in Japanese Patent Application Laid-Open No. 2003-018469.
However, in the solid-state image pickup device of the above described patent document, if the number of pixels to be added increases, the amount of charge accumulated in a memory 16 increases, thus resulting in an increase in output voltage. This causes the problem of difference in output range between at the time of addition and at the time of non-addition. An arithmetic operation unit provided outside the solid-state image pickup device performs correction such that an output amplitude range at the time of non-addition and that at the time of addition coincide with each other.